Robust Oxygen-Vacancy-Engineered Co(OH)₂/Cu Heterostructures Boost Nitrate Electroreduction to Ammonia beyond 2 A cm^-2.

Abstract

Electrocatalytic nitrate reduction reaction (NO₃RR) presents a sustainable paradigm for green NH₃ synthesis and NO₃ ^- wastewater valorization. However, overcoming sluggish NO₃RR kinetics under industrial-current operation persists as a critical challenge. Herein, robust oxygen vacancy-enriched heterostructures (O_v-Co(OH)₂/Cu) are engineered through in situ electrochemical reconstruction. By coupling Cu-mediated NO₃ ^--to-NO₂ ^- conversion with O_v-Co(OH)₂-accelerated NO₂ ^--to-NH₃ transformation, this heterostructured system delivers an unprecedented NH₃ yield rate of 167.8 mg h^-1 cm^-2 and 97.7% Faradaic efficiency at >2 A cm^-2, while maintaining exceptional current tolerance over 25 h. Operando spectroscopic characterizations and theoretical calculations reveal that the introduction of O_v in Co(OH)₂ synergistically accelerates water dissociation to ensure continuous hydrogen supply and optimizes ^*NOOH adsorption, reducing the energy barrier for the rate-limiting step (^*NO₂ to ^*NOOH). To demonstrate practical viability, a membrane-electrode-assembly electrolyzer integrating NO₃RR with glycerol oxidation reaction achieves highly effective co-production of NH₃ and formate alongside wastewater treatment. This work offers new insights into the rational design of electrocatalysts through in situ reconstruction-induced vacancy engineering for scalable and practical NO₃RR applications.